Electrical system for locating a sound source



Dec. 26, 1950 T. G. BARNES ETAL ELECTRICAL SYSTEM ECR LCCATING A SOUNDSOURCE Filed May 23, 1945 2 Sheets-Sheet 1 H. E m M m n ELEG rQ/cIMPL/Flea PUL SE 2 Sheets-Sheet 2 T. G. BARNES ET AL ELECTRICAL SYSTEMFOR LOCATING A SOUND SOURCE Dec. 26, 1950 Filed May 25, 1945 Mako- 4mP//NE law- MP /NvE/vroas T G, Barnes M J ELU-3er' 5) ATTOJQA/s/ ,4x/s aFSuf/Marey Patented Dec. 26, 1950 UNITED STATES sur OFFICE ELECTRICALSYSTEM FOR LOCATING A SOUND SOURCE Secretary of' War Application May 23,1945, SerialNo. 595,352;

7 Claims. 1 This invention relates to methods and. apparatus for themeasurement of time differencesv between impulses and more particularlyto sound direction nding and ranging.

One object of our invention is to provide a method for determining thedirection of a sound source and the range of' saidv sound source from axed position.

Another object of our invention is to provide suitable apparatus for,determining the direction and the range of a sound source from a iixedposition.

In present day sound ranging and direction finding systems and apparatussuch as used for locating theA position of enemy artillery of varioustypes it is the general practice to place a plurality of sound sensitivedevices along an extended base line that is substantially perpendicularto the line of direction of the point from which the sound is expectedto emanate. By observing the timev interval. between the sounds arrivalat the plurality of' sound sensitive devices thus situated, it ispossible to calculate the direction and rangeA of the soundu sourceVafter necessary correction is made for the effect of wind, temperature,and humidity, upon the speed and direction of travel ofthe sound throughthe atmosphere. Prior devices for measuring the time interval betweenythe arrival of sound waves at a plurality of" sound-sensitive deviceshave` been complicated and bulky; thus reducing their effectiveness inthe field; It`- is a further object of our invention to providea simpleand effective method' of measuring such time intervals so that a directindication may be obtained. It is still `another objectl of ourinvention to provide a simple and effective apparatus thatV will give` adirect measurementv of. the time interval between the. sounds. arrivalat each of a pair of sound sensitivedevices, combined with anv in'-dication of whichv soundsensitivei device received the sound iirst. Itis also an object of our invention that a plurality of the compositedevic's as described herein be used to determine the range as well'r asthe' direction.

Other-objects and advantages will become apparent in the followingspecication of embodiments Vof the inventionl illustrated` in theaccompanying drawings, wherein:

Figure 1Y is` aA schematic arrangement of our device.

Figure 5 is a schematic diagram of the. vac--y uum tube voltmetercircuit used in ourinvention.

Figure: 5 is a more complete schematic di agr-am of a device embodyingour invention.

Referring to Figure l which shows in scheA maticfashion the eldarrangement of our in,- vention, i is a source. of sound waveswhosedirection and range relative to the reference or base line is it isdesired to determine. Two or more sound sensitive devices such asmicrophones Ii:` and l2 are,r spaced apart on the base; line, usually atadistance ofabout 400 feetfron'r each other; Thisbase line distanceisnottcritical and any distance may be used within that from: whichreasonable accuracy may be expected.` The orientation of the baseline Ipreferably is such that the normal to the base line passes, through thatportion of territory in which the? sound source to` be located isbelieved' to be sit-- uated. The two microphones Il and I2 are connectedby lines |15 and IE to the time interval measurement means I 3. The timeintervalmeas urement means I3 gives an instantaneous reading, of thetime interval between the arrival ofV the sound at microphones` IlA andI2, as Well as. an indication as to which microphone received--thefsound first. Furthermore an indication; is.l given of the fact. whenboth channels receive4 impulses simultaneously..

Referring to.` Figure 2 which is a block di.- agram-of the entireapparatus it is seen that there' arel two symmetrical channels, one foreach. microphone. The: output of microphone Ill is.' fed into anamplifier Il', the output of. Whichis fed into a trigger circuit i9. Inalike manner ,the output of microphone I2 is amplied in amr-f plier I8andthen fed into trigger circuit 2t; The operations of; the triggercircuits i9 and 2'0;` each produce a4 change in theY ow. of a` direct:current,` which currents are. then combined in the timing` circuit 211|:to produce.t a pulse whose Figure 2 is a block" diagram of the entireap-- paratus.

duration is equal to the difference in the sound arrival times atmicrophones H and i2.

Figure 3 illustrates the sequence of operation inA eachportion of theapparatus shown in Figure 2. Approximate wave forms are shown forpurposes of illustration. Each microphone is poled in its connection tothe apparatus so that the compression part of the sound wave actuates itto produce a potential at the grid of the trigger tube which potentialis in the positive direction, thereby overcoming its bias potential.

AThe air wave strikes microphone I! at a time T1, and-the microphone I2at a time T2. The

frequency wind interference signals are suppressed, and applied to theirrespective trigger circuits which change the ow of direct cur rent asshown, beginning at Atimes T1, and T2 respectively. In the timingcircuit 2| the resulting potentials are combined to produce a pulsewhose duration is equal to the dierence (T2-T1) in the sound arrivaltimes at the microphones II and l2. The timing circuit 2l thereuponfunctions to provide a voltage proportional to the time diierence, whichvoltage is applied to the vacuum tube voltmeter 22.

Referring now to Figure 4 which is a simplified schematic diagram of ourinvention, the trigger circuit used will now be explained. This circuitcomprises a gas lled triode 23 that is normally nonconducting, and avacuum triode 25 that is normally conducting. Since our device has twosymmetrical channels, a duplicate trigger circuit for microphone l2 usesgas triode 24 and vacuum triode 26. Although the explanation thatfollows will pertain to one of the two symmetrical channels it is to beunderstood that the explanation applies equally as well to the otheridentical channel. Point 38 is maintained at 90 volts. Point 39supplying plate potential to tubes 25 and-26 is maintained at 1121A.;volts. When the gas tube 23 is not conducting point 34 will also be atthis potential of 90` volts. Since the potential at point 34 is morepositive than that of point 36; plate current flows in thevacuum triode'25. This flow of plate current establishes the potential level of thecathode of vacuum triode 25 at about 91 volts and the potential level ofpoint 35 at about '71 volts. The point 36 of the plate supply battery onthe vacuum triode remains at +45 volts above ground. The purpose of thetrigger circuit is to abruptly cut off the flow of current in 28 when apositive pulse from the amplifier I1 reaches the negatively biased gridof the gas tube 23 and causes the tube to strike. The instantthe gastube 23 breaks down, the potential drop across-it goes down to aboutvolts. When point 34 drops to +20 volts the vacuum triode ceases toconduct because the potential of point 35 cannot drop below +45 volts,and hence a 25 volt negative bias is impressed on the grid of tube 25.When tube 25 ceases to conduct it ceases-to draw plate current throughresistance 28, and the potential at point 35 drops to essentially thatof point 36, i. e., the potential across resistance 28 is reducedessentially to zero. This loss in voltage reacts on the timing circuitas indicated below.

The timing portion of our device operates in the following manner:Referring to the schematic diagram in Figure 4 it is seen that points Yand 31are initially at equal potentials of +71 volts. Condensers 32 and33 are connected to points 35 and 31 through charging resistors 33points 4'!) and tl are at equal potentials of approximately +71 volts.Upon the triggering action reducing the volta-ge across 23 to Zero itwill be observed that a potential diierence is established between 35and 3'5 in such a direction that the diode 27 becomes conducting but thediode 21' does not. Condenser 32 thereupon starts charging throughresistance 30 in order to equalize this potential difference. However,the :product of the condenser 32 and resistance 33, commonly known astheir time constant, is made large enough to reduce the charging rate tosuch a degree that the condenser 32 is never charged to more than 1/6 or1/8 of its ultimate potential duringa'ny time intervals which the deviceis intended to be required to measure. By these means the charge on 32wili be proportional within a very close approximation to the timeinterval during which the circuit is maintained in the condition tocontinue the charging action.

When the" sound impulse arrives at microphone I2 it triggers the othergas tube 2t thereby dropping the voltage across resistance 25 to zero.The'plate of diode 2 drops to +45 volts thereby stopping the charging ofcondenser 32, point 40 then being at a potential slightly greater thanvolts. Due to the unilateral conductance o tube 2l the charge is lockedon condenser 32.

Since no current has as yet flowed in diode 2lV both sides of condenser33 are at a potential of +45 volts. Thus point 4E) is left at apotential slightly higher than point di, this potential beingproportional to the time interval between the triggering of tube 23 andtube 24. This diierence inpotential is then indicated on a vacuum tubevoltmeter 22 of very high input impedance. Since this diiierence inpotential depends on the time interval between the triggering pulses,the vacuum tube voltmeter reading may be calibrated in terms of timeinterval.

At this juncture an automatic overload prevention feature will bedescribed. If the microphone l2 should be inoperative or the soundimpulses arriving thereupon be ofv a low energy level the actiondescribed immediately above would not occurand it might appear that thevoltmeter would be driven such as to increase the microammeter readingbeyond its full scale reading and possibly damage the instrument. Thatthis is prevented in one circuit may be seen with the aid of thefollowing tabulation where` in the potentials, at the several pointsindicated, are given in time sequence beginning with the triggering ofgas triode 23 and continuing through the triggering of the gas triode 24due to reception of a sound impulse by microphone l2. A nal column givesthe potentials existing at the several points if gas triode 2e' is nottrigand 3| respectively and are uncharged, since 60 gered.

TABLE Potentials at various times of triggering cycle At a great At tuneAt time A i'lias 'Twoffe- T2 Cm@- lt't Before m 'ered sponding spondingSecond Trigger tgsay to say full to triggerhamm time T1 scale of the ingof other cis not voltmeter channel Trggered Point 35- 7l 45 45 45 45Point 40. 71 70 70 48 71 Point 4L 7l 71 7l 45 71 Point 37.-- 71 7l 71 457l Junction 0I 30 & 32-.- 71 70 67 45 45 Junction 0f 31 6r 33-.- 71 7l.71 45 V7 1 tion.

acontece Referring tiief table the' nrst e'oliiiiirrA liststliiseveral?points whose' potentials are of iiiterestff atA this juncture;potentials at these points inthe standby coi-l:` dition-that is, upuntil the reception of the signal 01730, 32andthe"dode 21. Du'e to theplatelre# sist/ance of` diode 21, point 40' willV assume a poeptiipose's* the potential across the diodefistalefrr 'Y asll- Volt; Inpractice this potential drop will ordi- :lar-ilybeinA thevorder ofmagnitude of'orie'V-terlth` velt:- ItlV wil-l be seen that points 40 and4l? ow diiferin potential'bythis potentialdrop aridtlriatv point 4I ishigher. As the' flow` of' current con theV potential across thecondenserA 32 increases such that the potential at the' junctonl`tential is given as 67 volts. At thismoment it is assumed that theSecond channel is triggered.

examination of the potentials existing shows the condenser has beencharged to a difference of? potential off 3Y Volts; This approximates`-thel full" scalev reading or the instrument. At this saine` time due totheV trigger action of the second?- chan'nel point 37v is now caused todrop to +45.-

As a consequence no further action takes place (since point 35' also at+45) and current flow in diode 2feeases. Column 5 gives the potentialsexisting at the several points. It will be noted that since condenser 32was charged tothree volts pointllil` Will bethree volts higherthan thejunction of 30' and 32. Since this junction isnoW at +45 volts (currentflow has ceased' through 30)- point` 40 will be at a potential of +48.Comparing this with that of point 4| it will bei seen that point 40 ishigher by thev amountv orv charge induced on the condenser 32. Alsoasnote'd Ypreviously during t-he charging process' 4U was lower thanpointf 4l.

needle is constrained to movein a direction opv^l pls'ite` to its nalreading.

Refell'-g again to the table' thelastcolumn.

lists the potentials which obtain if the second cli'armel does nottrigger. points 4t and' 4t arenow of the same potentiar.

is` caused' by the fact' that the condenser.; Having.' been fullycharged, does not permit anyl further flow ofu current.I The potentialdrop acrossV` thediode`g21 is therefore reducedV to zero and points 40and 4l are at equal potential; Dur'- ixgff the course of.v suchhappenstance theA needle motion.' of the indicating instrument rapidlyappreaches zero reading. The speed at which the".

will;V not produce an "off scale meter reading.

thus avoiding' damage to the instrument.

Ina: similar manner. a time interval produced inithe' reverse" order,that is, for the sound str-ik'-` ing microphone l2 andA then microphoneIl. the final potential.' at point. 'l would exceed the finalpotentiallat point 40 by the proper amount.

Column two lists the- This actiongives' the meter reading a` very'characteristic mo During the charging period the meter' lit will benoted that voltx'neter :2i would; indicate: the I time inter-fval.; onthe: other'sideof: its center point. Thus thei algebraic sign as wellas? the magnitude of" the time? interval.. is given, thereby indicating`thef directionosoundsourcewith.respect to the normal. tothe' base line..

Referring to Figure 5 which.' is a schematic dia-v gram' of.' the:vacuum'` tubeV volt'meter 22,. it' is. seen-- that:tnevoltmeter'issofthe; cathode followertype.

Itl provides at substantially linear responseY over? a wi'clerange of"grid potential, over which range` iti-maintainsits-ihigh inputimpedance. Tnegrids of thel two vacuumA tubes' 42 and 43 are tied re`spectivellyto points 4,1)4 and: 4| ofithe' timing cir-V euitrsggvi. Theplate. current causes a.` potential.

dropacrossthe cathode? load: resistor which. en"-V ables the cathode tofollow the potential ofi the gridL Inord'er to: obtaina highinputimpedance itisnecessary'tc operatefthertubewith a negative grid'biasa-It has been foundthat'a large cathode load resistor coupled with alfairly high plate potential will cause the' bias to remain negati-veover a signal input range` of from' 0` to +100 volts, In general thecathodeV follower type of circuit provides the:` ideal manner forobtaining feedback; It is Well known thatv a high degree of` linearitymay be obtained when the product.-

of the'amplication factor and the percentageV feedba'cl'rv is large. vSSTL! which has a high amplication factor, may be used with excellentresults in this circuit. The dilerence in potential between the cathodesis measured with a microammeter 44 in series" with a high resistance tbreduce interaction be"- tween the two cathode circuits. This potentialdifference is a measure ofthe potential diierence'- existing at thegrids, which in turn is proportional tothe' charge trapped on one of thecondensers 32 or 33; This', as has been indicated above; is

L inv turn closely proportional to the timel interval` between soundpulses arriving at microphones Il and l2; Therefore, the potentialdifferencev at the'fcatho'des is a direct measure of the time interval',and for co'I-lveniencel the microammeter 44 maybe calibrated directly inmilliseconds.

When our? device is utilized inthe eld it becornesv necessary tomaintain the calibration oftheiins'tr-umentas' thebatteries` supplyingthe device become exhausted. The potential difference between points im7and lll` is a measure of the time" interval, providedA the normalvoltages across resistors 28 and 285 are-held constant. Thevoltf agesacross resistors 28 and 29 drop as the batteriesrun down, so a dualvariable resistor 45 andi dtis used` to resetzthe voltage values. (SeeFigure 6L) With the batteries at full charge the voltage acrossresistors 28` and29 is reduced. As the bat-- tery voltage: goes down,resistance inthe circuit is reduced by` means ofI dual variable resistor45 and 46 to keep the voltage across resistors 28 and 23 constant.

In calibration',` the rst step is to set the potential' across resistors28 and. 29 at alxed value: (say 26 volts). This isldone' by connectingthe mi'croammeter 44 and` a series. resistor across points 35 and136as'shownin` position A of switch.` 52', and operating the dual variableresistor 45 and 46" until` this potential is obtained.

Rotary switch 52 shown schematically in Fig. '7 may'v be" of theconventional wafer type having two'wafers and two circuits per waferwith three contaet positions` A, B and G for each circuit;

wafer.' are connected in all switch positions toof a' centen reading,meter in vacuum. tube.. ne terminals 55 andi 56 of. themicrcammeteif4'4- of For example, the tube type.

aseaaa Fig. 6, while the corresponding'contact arcs o-f the right handwafer are connected, in all positions to control grids 4l! and 4| oftubes 48 and 49. The numerals shown on the leads of the switch all referto corresponding numerals of Fig. 6 to which they are connected, theactual connections being omitted to avoid confusion. As the switch ismoved through the successive positions A, B and Cthe contact arrowsshown for position A move to corresponding positions B and C for bothwafers. Thus for position A, as shown, the contact arrows on the lefthand wafer connect the micro-ammeter 44 (with its included seriesresistor) across cathode resistor 28 at terminals 35 and 36 measuringthe potential drop thereof. ...Connections Afor otherrrpositions may betraced similarly.

'Ihenext step` is to adiust the vacuum tube voltmeter to zero. This isdone byoperating the switch 52 to position B and adjusting potentiometer53 until the meter reads zero. VIn this condition, the grids of thevacuum tube voltmeter tubes 48 and 49 are connected together and are ata potential of +45 volts. The third and nal step in the calibrationprocedure is to remove two forms of Vunbalance. rlhe first form ofunbalance is due to the fact that the potential across resistor 28 wasset accurately with the meter and across resistor 29 only approximatelybecause the dual control resistors 45 and 45 are not perfectly matched.The second unbalance is produced by the difference in emission potentialexisting .i in the diodes 2l and 21' when there is no external potentialapplied across them. This emission potential varies slightly from tubeto tube. By plac ing switch 52 in position C, and momentarily shortingcondensers 32 and 33 by switches 50, 5l any unbalance will be disclosedby the meter needle drifting to a new reading when the short circuit isremoved from condensers 32 and 33. Such drift is eliminated by operatingthe variable resistor 41, such that no variation in reading is obtainedwhen the switches 58, are operated. In this condition the position ofthe microammeter needle may be slightly displaced from the zero, butthis will have no eiect on the iinal reading because the slightdisplacement is caused by the fact that the grids are at +71 voltswhereas the vacuum tube voltmeter was calibrated at volts. Since the nalreadings are made with the grids at about +45 volts, the variationobtainedl when they are at .+71 volts is unimportant.

The gasv tubes 23 and 24 are deionized manually by introducing a largeresistance Si) between the cathode and ground by means of switch Elwhich is normally'closed. The introduction of a resistance instead of asimple opening of the circuit provides a leakage path for any chargeaccumulating on the cathode, and hence lessens surge potentials when theswitch is shorted again. Switch 38, normally closed, is an on and offswitch connecting a 90 volt source of potential to plates and grids oftubes 23, 24 and 25, 26 through suitable resistors respectively.

l Condensers such as 52 and 63 between the cathodes and the grids of thegas tubes 23 and 24, respectively, may be added for the purpose ofreducing the response of the device to high irequencies outside of therange normally utilized. These condensers also serve to reduce thetransient when the device is reset. Resistances 64 and 65 in thecircuits of thevgrids of these gasY tubes serve to reduce the effect onthese tubes of impulses received after either tube with, which theresistance is associated vhas triggered, thereby Neon tubes 66 and 61with their associated.

resistors 68 and 69, respectively, serve to indicate when the triggertubes have functioned. They are illuminated in the initial condition andeach,

isextinguished when its associated tube triggers. It is the purpose ofthese neon tubes to indicate whether or not a signal sufcient to causetriggering is received at both of the microphones.`

Without these tubes an extraneous signal triggering only one microphonewould give a false reading and a signal arriving at both microphonessimultaneously would give no visual evidence of the'd'evice havingfunctioned. Since that reading would represent a sound sourceapproximately on the normal to the base line the neon tubes eliminatethe loss of what would otherwise bean' entirely validV observation.

By Calibrating the scale of meter 44 directly milliseconds, a directreading may be had of the interval between the arrival times of soundenergy at microphones Il and I2.

The use as described above of two or more sets of equipment at separatedlocations along a front facing the source of ,sound energy will enablethe i determination of the line of direction of the sound source fromeach of the locations. By the method of intersection of these lines ofdirection the location or range of the source of sound may then bedetermined.

Further embodiments, modifications and variations may be resorted towithin the spirit of the invention as herein claimed.

We claim:

1. A device for measuring the time interval between the arrival of apulse of sound wave energy at two separated sound sensitive means from adistant soundsource, comprising means for con-` verting said pulse ofsound wave energy into an equivalent pulse of electrical energy at eachsound sensitivermeans, means for initiating a ow of electrical energy atinstant of rst pulse, means for stopping said flow at instant for secondpulse so that the duration of flow is equal to the diiierence in thesoundk arrival times at the said sound sensitive means, means to producea voltage ,Y

whose magnitude is proportional to said diner# ence in sound arrivaltimes, and means for in dicating the magnitude of said voltage, saidinitiating means including a gas discharge tube responsive to said rstpulse having a grid biased beyond cut-ofi and an anode resistorconnecting the anode to a source of positive potential, said stoppingmeans including a similar biased gas tube responsive to said secondpulse; said voltage producing means including a pair of normallyvconducting vacuum tubes having grids directV coupled to the anodes ofsaid gas tubes respectively, cathode resistors connected to a point ofpredetermined positive potential less than arbre-. said anode potentialsource, and anodeV connected to a common point of potential higher thansaidI predetermined potential; a pair of timing circuits bridged fromcathode to cathode of said vacuum tubes to receive the output thereof,each circuit including Vin, series a resistor, a condenser and a diodehaving its cathode connected to the condenser, oneV circuit having thesequence of ele.y

ments arranged in reverse order, whereby a charge proportional to thedifference of arrival;

times is accumulated on one of said condensers;

said indicating means including a vacuum tubeV at two separated soundsensitive means from-a distant sound source, comprising, meansfor `conyertmg `said pulses of sound `tvave `energy aiuto 'equivalent pulses of`electrical energwmeans `for zamplifryingsaid electrical energy, means`for 4pro- .:ducing. a :flow of electrical energy the duration of whichis .equal tothe difference in the sound .Wave f energyarrival times 4atthe said two sound `sensi- AtivemeanS,means for producingfromfsaid ,110Wa :voltage whose magnitude is proportional to ,said `'difference insound arrival times, and .means `to indicate the magnitude of saidvoltage andto'fin- .dig-:ate the sound sensitive means r#at .which 4theypulses of sound `Wave energy `arrived `first, said producing meansincluding 'a :pair of gas fdisfchargetubes responsive respectively tosaid 'sound ysensitivemeanshaving grids normally biased beyond .cut-offanodes energized through anode re- :sisters connected to a source ofpositive potential, and a :pair .of vacuum .tubes having Vgrids directcoupled to thegas'tube-anodes respectively, :and `-cathode resistorsconnected to a `point of predetermined positive potential less than saidgas "tube anode potential source; said voltageproducing means includinga pair -of circuits bridged from cathode'to eathodeof said pair ofvacuum Vgtubes, each .circuit includingi-nseries -a resistor, a

`condenser, anda diodehaving its cathodeconnected to the condenser, .oneoifsaid circuits hav- :iing the sequence of Velements arranged in`reverse order; said voltage indicating means including a! center zerovacuum tube voltmeter having :lnput :terminals connected to the cathodesof said diodes respectively, whereby the time interval is measured bythe voltmeter deflection and the order of pulse seouence is indicated bythe direction ,of the deection.

3. In a device of the classdescribed, comprising two symmetricalelectrical channels, each channel 'having a microphone, an amplifier,and

a, trigger circuit, said .tvvo microphones being f ,situated apart and.arranged v-to receive pulses of lsound .energy from a .distant soundsource,means :to apply the outputs of said trigger circuits successivelyto controlthe flow of charging current l'through `a timing condenser theduration `oi' :which is equal to the dilerence in arrival times -at themicrophones of sound energy pulses from said distant sound source, `andvacuum tube voltrneter means to indicate the voltage of saidtimingcondenser the magnitude of which is proportional to the differenceinrsaid sound arrival times; said trigger circuits including a pair ofgas discharge tubes located in the respective sound pulse responsivechannels having grids biased beyond cut-ofi and anode resistorsconnected to a source of positive potential; said trigger circuitapplying means including a pair of Vacuum tubes having grids directcoupled to the anodes of said gas tubes respectively, cathode resistorsconnected to a point of predetermined positive potential less than saidanode potential source and anodes connected to a common point ofpotential higher than said predetermined potential; said Vtimingcondenser circuit including a rst and a second circuit bridged fromcathode to cathode of said pair of vacuum tubes to receive the outputthereof, said rst circuit including in series a resistor, a timingcondenser, and a, diode having its cathode connected to the condenser,said second circuit being identical with lfirstcircuitfbut havingfthesequence of elements arranged in E.reverse order: said vacuum :tube

,forming a :trigger circuit, means -to apply .saidV trigger'circuitoutputs to produce a pulse of `elecftrical energy the .durationo-f which`is egual to the-said time interval, means to produce@i voltage the`magnitude-of which is `proportiQual to the said ,time interval, andvacuum ,tube vol-tmeter means to indicate the -;magnitude of SaidY,voltage and which `soundsensitive means first-received the-:soundwaveenergy; said trigger -circuits ,including a y,pair of ,gas dischargetubes 11o- Acated in .the Arespective ysou-nd pulse rresponsive'channels havinggridsbiased beyond cut-offend anode resistors ,connectedto a source of `positive .fgpotentiah said .trigger circuit 4,outputVapplying means ,including a pair of `vacuum tubes having ,grids4,(.iirsctcoupled to the yanodes ofsaid .gas :tubes:vspectivelv,cathode.resistors connected@ apontyof predetermined positivepotential 'thanf'saidzainode potential Source and anodes.connectedtofapoint of potential higher thansaidpredeterminedfpotential; said time Vinterval volt-- age producing means`includinga pairof timing circuits :bridged lbetween the cathodes `,of`said vacuumtubes,eachsaid circuit including in series aresisteugatmingcondenser, and a diodehav- `ing f-its .cathode `connected -.to thecondenser, one ,of said Acircuits havinglthe sequence of `,elementsarrangedin `the-reverse order; said vacuum tube yoltmetenincluding a`pair-.of vacuum-tubes hav- ;,ing cathoderesistor grids connectedrespectively ,tothefcathodes fof lsaid timing` circuit f diodes and acurrent indicating meter having input term-inals vconnected .to theY,catnodes .of said pair of .vacuum tubes..

.5. device Iormeasuring the time interval between the Iarrival orf-soundwave energy .at .two separated Vsound vsensitive means 4from Va .distantsound source, comprising means for converting the sound -waveene1gyarriving at -each Aof said .sound sensitive `.means A,intoelectrical energy, .means forming two ysymmetricalelectrical -c-hasnels. one.forfeaeh-.sound-sensitive means, an1amfslinerfforfeachfofsaidchannels, a triegereircuit including a gasdischarge tube for each of said channels, means to deionize said tubes,pulse timing means to combine said trigger circuit outputs to produce apulse of electrical energy the duration of which is equal to said timeinterval, means to produce a voltage the magnitude of which isproportional to said time interval and means to indicate the magnitudeof said voltage, said trigger circuits including a pair of gasdislcharge tubes having grids biased beyond cut-off and anodeI resistorsconnected to a source of positivepotential; said pulse timing meansincluding a' pair of vacuum tubes having grids direct coupled to theanodes of said gas tubes respectively, cathode resistors connected to apoint of predetermined positive potential less than said anode potentialsource land anodes connected to a pointof"`potential higher than saidpredeterincluding in series a resistor, a condenser, and a a diodehaving its cathode connected to the condenser, said second circuit beingidentical with first circuit but having the sequence of elementsarranged in reverse order; said voltage indicating j means having inputterminals connected to the cathodes of said diodes respectively.

6. A device for measuring the time interval between the arrival of soundwave energy at two separate microphones from a distant sound source,Ycomprising means including two syln` `metrical electrical channels,'onefor each microphone, and an amplifier for each channel, a triggercircuit for each channel including Va normally 'non-conducting gas tubeand a normally conl ducting vacuum tube, means to apply said trig- ,3'ger circuit outputs to produce a pulse of electric current the durationof which is equal to said "time interval, timing condenser means toproduce from said pulse a voltage the magnitude of which is proportionalto said time interval, and a vacuum tube voltmeter to indicate themagnitude vof said yvoltage and which of said microphones rst receivedthe sound wave energy, said trig- 1 ger -circuit gas tubes located ineach channel having grids biased beyond cut-'01TJ and anode resis torsconnected to a source of positive potential; -fsaid trigger -circuitoutput applying means in- 1, cluding a pair of vacuum tubeshaving gridsdif rect coupled to said gas tube anodes respectively, fcathoderesistors connected to a point of predetermined positive potential lessthan said anode potential source, and anodes connected to acommon pointof potential higher than said predetermined potential; said timingcondenser means including a pair of similarhtiming circuitsbridged4between the ,cathodes of said pair of vacuum tubes, each said circuitincludingin series a rei' sistor, a, timing condenser and a'diode havingits cathode connected to the condenser, one of said i circuits havingthe sequence of elements arranged in reverse order; said vacuum tubevoltmeter includi-ng a pair of vacuum tubes having cathode resistorgrids connected respectively to the cath- 'Y odes of said timing circuitdiodes and a center Zero current indicating meter having input terminalsconnected to the cathodes of said pair of vacuum tubes.

7. A device for measuring the time interval between the arrival of asound wave at two sound or impulse sensitive devices comprising twosym-v metrical electrical channels, each channel being associated withone of the sound or impulse sensitive devices and eachv having anon-restoring-trlgger circuit connected to a common pulse timing circuitin such manner that the rst channel to receive an impulse starts a flowof electric cur rent and the second channel to receive the impulse stopsthe ilowV of said electric current, either channel being capable ofacting as a first cha-nnel or as a second channel in thefsequence ofoperations, timing condenser means to produce a voltage whose magnitudeis proportional to the duration of the ow of said electric current andwhose polarity depends upon which channel first received an impulse, andmeans for indicating the magnitude and polarity of said voltage, saldmeans being calibrated to read directly in time difference and toindicate the sequence of operation of said channels; said non-restoringtrigger circuits including a pair of gas discharge tubes located in therespective soundpulse responsive channels having grids biased beyondcut-off and anode resistors connected to a source of positive potential;said pulse timing circuit including a pair of vacuum tubes having gridsdirect coupled to the anodes of said gas tubes respectively, cathoderesistors connected to a point of predetermined positive potential lessthan said anode potential source, and anodes connected to a common pointof potential higher than said predetermined potential; said timingcondenser means inciuding a pair of similar timing circuits bridged'between the cathodes'of said pair of vacuum 'in reverse order.

tubes, each said circuit'including in series a resistor, a timingcondenser and a diode having its cathode connected to the condenser, oneof said circuits having the sequence of elements arranged THOD/[AS G.BARNES. MICHAEL J. BURG-ER.'

REFERENCES CITED Y rEhe following references are of record in the le ofthis patent;

UNITED STATES PATENTS Date

